Macro get_ref::impl_get_ref

macro_rules! impl_get_ref {
    (<$($TT:ident: $TTP:ident),*> $T:ty) => { ... };
    (<$($TT:ident),*> $T:ty) => { ... };
    ($T:ty) => { ... };
    ($($T:ty),*) => { ... };
}